The present invention relates to a powder either as a blend or as a composite which is particularly useful to produce by plasma spray technique, a bearing surface of high wear and scuff resistance. The present powder compositions are particularly useful in producing bearing surfaces on piston rings or apex seals in internal combustion engines, e.g. diesel engines or gasoline engines.
An alloy coating on a piston ring, or an apex seal in a rotary engine, encounters conditions not common to other bearing surfaces. Other bearing surfaces, e.g. crankshaft main and crank/rod bearing surfaces, are subjected to a rather uniform temperature in an oil bath, but with contact surface pressure variations. A piston ring bearing surface on the other hand must withstand a wide variety of conditions. These include wide temperature variation, wide pressure variation, exposure to reactive chemical products of combustion, minimum lubrication as compared to crankshaft bearings, for example, exposure to abrasive foreign particles, etc. Hence, an alloy that may be suitable in one environment is not necessarily suitable in another. The piston ring is a primary example. Often, however, a material which is able to withstand successfully the numerous conditions imposed on a piston ring in an internal combustion engine, will withstand the conditions imposed by another environment not only in an internal combustion engine, but elsewhere.
In the past, sophisticated coatings as bearing surfaces have been developed ranging from hard metals (U.S. Pat. Nos. 3,539,192; 3,690,686; 3,725,017; 3,814,447) to refractory metal oxides (U.S. Pat. Nos. 3,697,091 and 3,794,334). Each has its particular advantage in a given environment either in terms of processing or final use. One particularly useful material based on molybdenum is that described and claimed in U.S. Pat. No. 3,690,686 and is today in widespread use on piston rings for internal combustion engines. Its principal problem is one of economics as the price of molybdenum has risen as much as 20% in the last three years. Consequently, the initial powder cost is very high. About one-half of the plasma applied material is ground off in finishing piston rings coated in accordance with U.S. Pat. No. 3,690,686, and although there are reclaim values in the resulting sludge, the cost difference is also high. There is need, therefore, for a less expensive substitute for the high cost, high molybdenum content coatings.
Alloy bearing surfaces composed of molybdenum together with a substantial amount of iron and applied by plasma spray techniques are not broadly new. Reference may be had, for example, to the patent to Ingham U.S. Pat. No. 3,819,384 wherein a powder containing from 50 to 75% molybdenum and 50 to 25% of iron is taught as useful for the coating of piston ring surfaces. Also U.S. Pat. No. 3,991,240 teaches the provision of bearing surfaces formed from a flame spray powder including cast iron, molybdenum and boron. German Pat. No. 2,456,238 also teaches a composition formed from a powder containing iron, molybdenum and boron.
Iron, molybdenum and silicon containing systems as alloys are old, and in such systems a relatively wide range of silicon concentrations is known. Howardton, U.S. Pat. No. 2,383,969 teaches a permanent magnet containing 70% iron, 17% molybdenum and 0.1% silicon. Holtz, U.S. Pat. No. 3,655,365 teaches a tool alloy of 20-48% iron, 25-50% cobalt, 10-40% molybdenum, 0.5-4% carbon and a minor amount of silicon. The alloy is formed by the hot consolidation of three alloyed powders. Iwata U.S. Pat. No. 3,856,478 shows a valve seat alloy composed of 10-12% molybdenum, 88-90% iron and 0.05-20% silicon.
Slightly higher concentrations of silicon are shown in Flanders U.S. Pat. No. 2,124,877 for a hard tool alloy. The concentration of molybdenum is from 4.5-10%, silicon from 0.2-1.25%, and the balance iron. The presence of carbon, sulfur, phosphorus and manganese is also shown. Other references showing alloys with intermediate concentrations of silicon, include Wissler U.S. Pat. Nos. 2,219,462 and Scott 2,354,147.
Higher concentrations of silicon in alloys are shown in Yurasko U.S. Pat. No. 3,428,442. This composition contains a relatively small amount of molybdenum, i.e. 0.0-5.0%. Dechtold U.S. Pat. No. 3,161,948 teaches a low melting composition including iron and molybdenum along with silicon in the amount of from 5-25% by weight. Jerabek, U.S. Pat. No. 2,289,365 teaches a phosphorus, silicon, iron alloy which may contain molybdenum in amounts up to 35% by weight. The phosphorus/silicon is present to a maximum of 26% with the phosphorus ranging from 2-13% and the silicon from 6-22%. The balance is iron. German Pat. No. 2,433,814 also teaches an iron, molybdenum, silicon composition with 45% or less iron.
No prior art is known showing a powder blend or composite for plasma spray application to form a bearing surface which comprises 70-87% iron, 10-25% molybdenum, 0.5-6% silicon, 0.0-4% carbon and optionally, an organic binder in the amount of 0.0-2 5%, total 100%.
The present invention provides such a composition. A relatively small amount of the high cost molybdenum is used in combination with a mixture of iron and a small amount of silicon, optionally along with a small amount of carbon. Thus it has been found that in a piston ring or apex seal coating, iron can be used in combination with a small amount of silicon as an inexpensive extender for high cost molybdenum without substantial sacrifice of the properties of the high concentration molybdenum coatings.